CHAPTER 2 PLANT BREEDING PC Series

Transcription

1 CHAPTER 2 PLANT BREEDING 2. Introduction 2.1 Field Evaluation Trials The aims of the plant breeding program are to produce new, high yielding and high quality vegetatively propagated (VP) cultivars and composite plants that are adapted to local conditions. This is achieved by crossing selected parental stocks of cultivars and plant selection based on ease of rooting, quality, yield and easily rooting invigorating rootstocks and high quality scions VP cultivars for the production of superior composite plants. During the period under review, controlled cross pollinations were carried out using a wide range of plant material, and selections from these crosses were screened for quality, rooting potential, field tolerance to drought, extreme tem~eratures and pests and diseases. In I addition, drought tolerant invigorating PC Series Two rainfed field trials, one at Mimosa Research Station (MRS) and the other at Thyolo Research Station (TRS), were planted in December 1983 and 1985, respectively, to evaluate field performance of PCs in comparison with SFS 150 as a control. As shown in Table 2.1, PCs 137, 142 and 144 compared very favourably with SFS 150 in yield, with PC144 being outstanding in both trials. PC 133 yielded better than SFS 150 at TRS whereas the opposite was true at MRS. However, all of these four cultivars have a quality potential only similar to SFS 150, and their erect leaf poise renders them unsuitable for mechanical harvesting. Table 2.1. Mean made tea yield (kg ha') over five years ( and ) and rootstocks for the production of quality valuation as a Percent of SfS 150 composite plants through grafting were value of PC series at Mimosa and produced. The selected materials were Thyolo. evaluated for yield production in the multilocation final evaluation field trials in Malawi, Zimbabwe and South Africa. In Malawi, expert tea tasters also evaluated some of the potential cultivars for made tea quality potential using cultivar SFS 150 or PC 108 as a benchmark. I Mean This report highlights results d.l. from trials of progeny cultivars (PC) of different series in Malawi \ 3 and Zimbabwe during the period I under review. Details of materials and methods of the experiments were presented in the previous annual reports. Although none of the four promising cultivars were recommended for commercial cultivation, they were being evaluated as rootstocks for the of composite plants. I

2 PC Series PC Series In December 1987 a trial was planted at TRS to evaluate PCs in comparison with PC 108 and SFS 150 under irrigation. Results obtained showed that PCs 152 and 153 had a very high yield potential, outyielding both PC 108 and SFS 150. PC 151 also performed well, out yielding SFS 150. Unfortunately they only had average quality potential, as compared to PC 108 (Table 2.2). Table 2.2. Mean made tea yield (kg m. t. ha') from 1994 to 1998 and made tea quality valuation as a percent of PC 108 value of PCs series at TRS. In the trial that was planted at TRS in December 1987 to evaluate field performance of PCs using PC 108 and SFS 150 as standards, PC 160 yielded highest and out yielded PC 108 and SFS 150. The cultivar however, made average quality black teas, just edging over SFS 150 (Table 2.3). Table 2.3 Mean made tea yield (kg ha*) of seven cultivars over four seasons from and made tea quality valuation results as a percent of PC 108 value at TRS. These results showed that PC 153 has a higher yield potential than SFS 150. The cultivar also exhibited good offseason shoot development and could be a good alternative to SFS 150 in cooler tea growing areas. Also, PC 152 and PC 153 (also coded as RC 15 and RC 7, respectively) performed very well as rootstocks and were provisionally released as rootstock cultivars in 2000 / 1. These results showed that none of the above cultivars was suitable for commercial cultivation because of poor quality of made tea in comparison to SFS PC Series Three trials, two at MRS and one at TRS were established between 1987 and 1989 to evaluate yield and made tea quality of PCS As shown in Table 2.4, PCs 165, PC 168, 171, 172 and 173 had a high yield potential, comparing very well with, and / or outyielding PC 108 and SFS 150. In addition, PC 168 had a very high made tea quality potential with a value of USc 140 kg'. This value compared very favourably

3 with PC108. It was also found very suitable for machine plucking because of its horizontal leaf poise. Table 2.4. Mean made tea yield (kg ha') over five years from 1995 to 2000 of PC cultivars at MRS and TRS and made tea quality valuation as a percent of PC 108 Cultivar PC 161 PC 162 PC 163 PC 164 PC 165 PC 166 PC 167 PC 168 PC 169 PC 170 PC 171 PC 172 PC 173 PC 108 SFS 150 MRS Trial Made Tea Yield MRS Trial N/ A TRS Valuation (%) n/a n/a n/a n/a n/a 86 n/a Mean S.E CV% PC Series Two rainfed trials, one at MRS and the other at TRS, were planted in December 1989 to evaluate PCs The control entries were PC 108 and / or SFS 150. At MRS nearly all new cultivars, except PC 178, highly out yielded PC 108, with the best yields from PCs 175,176,177 and 182 (Table 2.5). At TRS there was no significant difference between PC 108 and the promising cultivars PC 175 and PC 182, all of which significantly out yielded SFS 150. All four new selections lacked good quality. PCs 165, 168 and 175 were formally released for fullscale commercial cultivation.

4 Table 2.5. Mean made tea yield (kg ha') Table 2.6 Mean made tea yield (kg ha') over five years from 1995 to 2000 of PC ofpc 183 to PC 199 over five seasons and at MRS and TRS and made tea annual yield of the season and quality valuation as a % of SFS 150 value made tea quality valuation as a percent of PC 108 value PC Series In an irrigated trial planted at Nsuwadzi Research Station in December 1998, cultivars PCs 184, 185, 186, 187, 193 and 199 had high yield potential as compared to PC 108 (Table 2.6). Their quality potential, however, was below that of PC 108. PCs 187, 193 and 199 have had erratic rooting performance in the nursery. PC 198 is easy to root, and has good offseason shoot growth, which could result in, extended cropping season. PCs 184, 185 and 198 have since been formally released for full scale commercial planting. Mean PC Series An irrigated trial comprising PCs , using PC 108 and SFS 150 as control cultivars, was planted at Nsuwadzi Research Station in December The results in Table 2.7show that in 2000/1 and over the fiveyear period, PCs 206, 213 and 218 yielded higher than PC 108 and SFS 150. PCs 206 and 213 also had very good cool season growth. In addition, PC 213 had a high degree of drought tolerance. However, the madetea quality potential of PC 206 was inferior to the quality potential of the two controls. PC 213 has since been formally released for full scale commercial planting.

5 Table 2.7 Mean made tea yield over five Table 2.8 Made tea yield (kg ha1) in seasons from and the yield in and cumulative yield (kg) over season (kg ha') of PC five year period from 1997 to 2001 of PC series and made tea quality valuation as series under irrigation at Jersey, a percent of PC 108 value. Zimbabwe. Cultivar Yield in 2000 / 01 Cumulative Yield EJULU KC PC PC PC PC PC SFS PC PC PC TN14/ WT PC Mean 6539 S.E. 232 CV% PC Series Table 2.8 presents yields from a trial established in February 1995, which was aimed at evaluating the performance of new TRF cultivars (PCs ) under irrigated conditions at Jersey Tea Estate, in Chipinge area, Zimbabwe. PC81, followed by PC 108, PC 114, WT 90 and TN 14 / 3, generally yielded very well relative to SFS 150, with PC 81 producing a total of more than 23t made tea ha1 over the past five seasons. Ejulu had the lowest yield in 2000 / 1 season. It can be concluded from these results that all cultivars, probably apart from Ejulu had high yields, particularly PC 81, PC 108 and WT 90, and were suitable for Jersey area PC Series at Zona, Chipinge The yield results from the irrigated trial at Zona show that PCs 140 and 206, followed by PC 217 and PC 144, produced the most crop over the past five seasons (Table 2.9). Furthermore, PCs 140 and 206, together with PCs 159 and 202, gave the highest yield in growing season. However, quality screening in Malawi showed that these cultivars, except PC 217, which requires further screening, had average quality potential.

6 Table 2.9 Made tea yield (kg ha') in and the cumulative made tea yield (kg) of PC series under irrigation at Zona, Zimbabwe. Clone Yield in Cumulative yield PC PC PC WT PC PC PC PC PC PC PC PC PC PC SFS PC PC PC PC PC PC PC PC PC PC PC Mean 4928 S. E. 467 CV % / 155 PC / PC201 SFS150 PC223 33/ / 237 PC186 33/ / 1720 PC131 PC14 PC111 33/2312 PC158 PC / 239 PC202 PC216 PC160 PC195 PC220 PC199 PC203 PC159 PC224 Although PCs 137,140,144, 159,202 and 206 had PC222 a high yield potential, their average made tea PC218 quality was unsuitable for commercial PC221 cultivation while PC 217 required further PC213 screening for made tea quality. PC144 PC PC series at Clearwater, PC212 PC141 Chipinge PC192 PC148 In an irrigated trial planted at Clearwater, PC140 several cultivars including , PC 137, PC PC , PC 219, PC 217, PC 144, PC 221, PC 148, PC 33 / , PC 141, PC 212, PC 213 and PC 206 PC152 compared very well with both PC 108 and SFS PC219 PC in yield potential (Table 2.10). However, they Mean needed to be evaluated at other sites in SE Zimbabwe to check on their adaptability. CV% Table 2.10 Mean made tea yield overfive year periodfrom to and yield in 2000/01 season (kg ha') of PCs 135 to 224 under irvigation at Clearwater, ~hbabw;. Cultivar 1 Yield in Mean yield PC

7 Promising cultivars 33 / 1541, PC 137, PC 152, PC 219, PC 217, PC 144, PC 221, PC 148, PC 140, PC 141, PC 212, PC 213 and PC 206 had to be evaluated further in properly designed field trials in Honde Valley. 2.2 Composite Plants Trials of composite plants to assess congeniality between rootstocks and scions and evaluate their field performance were planted in Malawi and Zimbabwe. Tables 2.11 to 2.13 show the results by the scion used PC 105 Composites in Malawi. Two trials were planted to evaluate PC 105 scions grafted on different rootstocks in Mulanje under rain fed conditions. The first trial was planted at MRS in December 2005 and the second one at Esperanza Tea Estate in December The results presented in Table 2.11 show that PC 105 produced highest yields when grafted onto released rootstocks RCs 2, 4 and 6, as well as on rootstocks RCs 7, 13 and 16. Table 2.11 Made tea yield (kg ha' in and cumulative yield over five yearsfrom 1997 to 2001 (kg) of PC 105 grown on diflerent rootstocks. S.E CV% Note: Figures in parentheses are percentage of the yield of ungrafted PC 105

8 These results suggested that PC 105 would best be utilised as a scion when grafted on the released rootstocks RCs 2, 4, 6, 7, 13, 15 and 16. Rootstocks 7, 13, 15 and 16 performed very well and were earmarked for release as rootstocks to PC 105 scions PC 108 Composites in Malawi Three trials were planted between 1994 and 1996 to evaluate the performance of PC 108 under rain fed conditions when grown on different rootstocks. Two trials were planted at MRS and the third one at Esperanza. PC 108 had marginal yield benefit when grafted on RC1, RC 4 and RC. 6. However higher yields were obtained with PC 108 as a scion on rootstocks RCs 7, 13 and 15 (Table 2.12) Table 2.12 Made tea yield (kg ha') of PC 108 grafted on difserent rootstocks in and cumulative yield (kg) over the period Rootstock PC 108 RC 1 (MFS 87) RC 2 (PC 87) RC 3 (77) RC 4 (14 22) RC 6 (PC 141) RC 7 (PC 153) RC 12 (R5 193) RC 13 (RS 233) RC 14 (RS 245) RC 15 (PC 152) RC 16 (22 70) RC 17 (29 36) RC 18 (29 44) JRS 7 RS 9 PC168/RC4 PC 183 (own) PC 185 (own) Trial 1 Yield in I Cumulative Yield I Trial 2 Yield in I Cumulative Yield I Trial 3 Yield in Mean S.E CV% I Cumulative Yield 5858 * ,

9 These results suggest that PC 108 should be grafted on rootstocks RCs 6, 7, 13 and 15 for maximum yield benefit from grafting. The encouraging results of rootstocks 7, 13 and 15 suggest that they should be released for use with PC 108 scions PC 114 Composites in Malawi. The performance of PC 114 as composite plants was evaluated under rain fed conditions in two trials at MRS in Mulanje. The results in Table 2.13 show that PC 114 performed better when grafted than when planted as a straight cultivar. Best yields were obtained when PC 114 was grafted on rootstocks RCh42, 3, 4, 6, 12 and 18 (Table 2.13). Table 2.13 Made tea yield (kg ha') in and cumulative made tea yield over four years (kg) of PC114 grown on difserent rootstocks. Rootstock PC 114 own RC 2 RC 3 RC 4 RC6 ' RC 12 RC 16 RC 17 RC 18 PC 168 on RC 4 Trial 1 Yield in , Cumulative Yield 7647 (100) 9253 (121) 8947 (117) 9406 (123) 9482 (124) 9865 (129) 8106 (106) (131) Mean S.E. i CV% Trial 2 Yield in Cumulative Yield 8542 (100) (131) 9259 (108) 9935 (116) (123) 8785 (103) 8654 (101) 9199 (108) Note: Figures in parenthesis are percentages values of the ungrafted PC 114.

10 2.2.4 PC 105 Scions at Clearwater in Table 2.15 Made tea yield in (kg ha Zimbabwe l) of PC 108 and PC 117 composite plants at EHPL, Zimbabwe In the irrigated trial at Clearwater, PC 105 grafted on rootstocks RC 6/20 7 and RC 7 together with ungrafted SFS 150. performed well relative to those grafted on control rootstock RC 2 (Table 2.14). Rootstocks RC 3, RC 16 and also performed well. Table 2.14 Made tea yield in (kg ha') and cumulative made tea yield (kg) of PC 105 composite plants at Clearwater, Zimbabwe Composite PC 1081 RC 16 PC108/ PC185 PC 1081 NVS 10 PC 1081 RC 5 PC 1081 RC 4 PC 1081 RC 3 PC PC PC 1081 RC 7 PC 1081 RC 6 PC 1171 PC 183 PC PC 1171 RC 4 PC1171 RC 7 PC1171 RC 5 PC PC 1171 RC 6 PC 1171 NVS 10 PC117/ PC207 PC 1171 PC 185 PC 1171 RC 2 PC1171 RC 3 Yield PC 108 and PC 117 Composites at Eastern Highlands Plantations Ltd, Zimbabwe. In the rainfed field trial established in January 1999 at Eastern Highlands Plantations Ltd., to evaluate the performance of different rootstocks using PC 108 and 117 as scions, PC 108 performed well on rootstocks 29 36/29 44, RC 6 and RC 3 but poorly on RC 16 and PC 185 whereas PC 117 performed well on RC 2, RC 3 and PC 185 rootstocks (Table 2.15). Mean SE CV% Although it was too early to comment on the results, it looked certain that these two scion cultivars have different specific rootstocks for maximum yield benefit from grafting. At this stage, PC 185 seemed very unsuitable for PC 108 but very suitable for PC 117 as a rootstock at EHPL. The trial was decided to run to maturity before any conclusive statement can be made about which rootstocks are most suitable for these scion cultivars at EHPL. 2.3 Top working The advantages of top working had been demonstrated during TRF field days and

11 the tea growers appreciated the benefit of this technology but had not adopted it. Resistance by the tea growers to adopt the technology was attributed to its low labour productivity. An experiment was, therefore, started in August 1999 at Nsuwadzi Research Station on established PC 81 bushes to determine practices that could increase the productivity of the grafter and reduce grafting costs. The following practices were studied: Use of the tea bush supplemented with grass to provide shade to the grafted stern Tying moist moss around the graft with a plastic strap followed by covering it with a moistened polythene bag and secure with a plastic strap. The results on number of scions grafted per manday, total number of scions grafted and success rate for each method show that bypassing putting moist moss around the graft union area (TI) significantly raised grafter productivity by 65% with a success rate of about 80% (Table 2.16). Table 2.16, Grafter productivity as measured by the number of grafted scionslmanday and success rate measured by the number of scions with union formed of grafted scions. Water Method retention TI TZ Mean SE CV% Average number of scions /manday Total scions Grafted scions Successful scions Q 423 (80) 242 (76) The increased labour productivity and very high success rate in the formation of the graft union arising from bypassing the moist moss stage was a welcome outcome. Bypassing the moist moss stage led to considerable reduction in grafting costs since there was no need to look for moss or purchase any water retaining material and grafting tape.or plastic straps for securing the moist moss around the graft. High labour productivity of 132 scions (equivalent to 33 bushes) per manday suggested that only mandays were required to upgrade one hectare as opposed to mandays with the conventional moist moss method. Furthermore, this modified method showed potential to increase success rate even further because of minimum handling of the scion and, therefore, minimum risk of disturbing cambium alignment after inserting it into the rootstock cleft. The exclusion of moist moss had however added costs because without the moist moss the frequency of replenishing moisture in the bag was higher and involved more mandays. Since bypassing the use of moist moss does not save labour, there is need to explore other and cost effective means of ensuring high humidity in the graft bag. 2.4 Shoot Growth Studies New TRF cultivars yield very high under experimental conditions but do not yield as high under growers' conditions. A number of factors contribute to this discrepancy. Some growers use poor sites for their tea and/or do not prepare land adequately and timely, and generally employ suboptimal crop husbandry practices. The other factor, Ghich has been reported to contribute to the low yield levels of TRF cultivars under growers' conditions, is the shoot age at the time of plucking. Tanton, 1979; Cannell et al;

12 1990; Steph &I s and Carr, 1993 have reported thatthe optimum time to pluck is when shoots have just accumulated adequate dry matter required for black tea quality Previous work at TRF has established that in the main cropping season from December to April in Malawi when growing conditions are optimum, shoots of seedling and old cultivars take on average 42 days to reach pluckable size. This information is not known for new TRF cultivars., 1 Studies on shoot growth were therefore started in growing season to determine the optimum plucking timeof shoots from some new cultivars such as PCs , PCs , and PCs series, together with composites derived from PC 105, PC. 108'and PC li4. Shoot length from day 21 to day A9 following thk removal of apical dominance (plucking) was measured. Results below are preszfited by ' th'e' cultivars. mid December to first week of February took about 42 to 49 days to reach pluckable size while those generated in mid May were still too small to be plucked at day 49. PC 110 showed the most shoot extension growth, followed by PC 81 when shoots were generated on /98. There were no marked differences between PC 105, PC 108 and SFS 150 at day 42 and day 49. When shoots were generated on 29/01/99, PC 110 and SFS 150, followed by PC 81, showed the most extension growth, while PC 105 and PC 108 again showed the least growth at day 42. When shoots were generated later on 09 / 02 / 99, PC 110 showed the most shoot extension growth followed by PC 81 and SFS 150, with PC 105 and PC 108 showing the least growth at day 42. Shoots generated in May had SFS 150 and PC 81 showing the most shoot extension growth followed by, PC 110 and PC 105, with PC 108 again showing the least growth, d a) PCs As shown in Figure 2.1, shoots generated early in the main growing season from 0 Day Day Day Day Day, Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Figure 2.1. shoot length (mm) of PCs 104,105,108,110,81 SFS 150 at three dates of shoot initiation

13 b) PCs 165 and 168 The results in Figure 2.2 show that for shoots generated in the main growing season between December and early February, PC 165 and PC 168 (those generated on 28/12/98), or PC 165 followed by PC 168 (those generated on 28/01/99), showed the most shoot extension growth followed by PC 108, with SFS 150 showing the least growth at day 42 whereas for shoots whose growth was initiated in March/ April PC 165 and PC 168 again showed the most growth but the least growth was shown by PC108, though they were all too small for plucking even at day 49 for those initiated at the end of April. 0 Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Figure 2.2. Shoot length (mm) of PC's 165 and 168 compared with PC 108 and SFS 150. Date shown is date of shoot initiation PCs 184,185,198 and 213 As shown in Figure 2.3, i PC 198, together with PC 185 and PC 213, had the most shoot extension growth, followed by PC 184 and then PC 108 or PC 108 and SFS 150 together in the main season. In the cold season, PC 198, PC 213 along with PC 185 again showed the most shoot extension, followed by PC 184 and SFS 150, both producing significantly more growth than PC /2/99 X 23/2/99 )c 15/3/99 15/4/99 Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day PC184 0 PC185 X PC198 PC213 +PC108SFS150 Figure 2.3. Shoot length (mm) of PCs 184,185,198 and 213 compared with PC 108 and SFS 150. Date shown is date of shoot initiation

14 d) PC 105 composites This was rainfed young tea planted in December 1995, and the bushes were last pruned on 01 / PC 105 grown on the root systems of different rootstocks was compared with the ungrafted. The results presented in Figure 2.4 show that for the shoots generated on 04 / 02 / 99 there were no significant differences in shoot extension growth between ungrafted PC 105 plants and those grown on rootstocks at day 42, though those on RC 1 were slightly longer and those on RC 3 slightly shorter than the ungrafted ones. In the cold season there were no differences in shoot length at day 42 except for those grown on RC 3 which had the least shoot extension growth. 4/2/99 12/4/99 Day0 Day 21 Day 28 Day 35 Day 42 Day 49 Day 21 Day 28 Day 35 Day 42 Day 49 Figure 2.4. Shoot length (mm) of PC 105 composites compared with ungrafted PC 105. &g >s.a x ;c e) PC 108 composites 3 In the cold season, however, the un 2. & As shown in Figure 2.5 there were grafted PC 108 plants had the least. generally no significant differences at day growth, much less than those grown on + 42 between ungrafted PC 108 plants and RC 1, RC 2 and RC 4 rootstocks, A + 2 those grown on rootstocks in the main particularly at day 49. PC 185 showed growing season. Composites of RC 2 more growth than all PC 108 plants, both and/ or RC 6 tended to exhibit less growth in the main growing season and in the than those ungrafted. cold season. Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Day Figure 2.5. Shoot length (mm) of PC 108 composites compared with ungrafted PC 108.

15 f) PC 114 composites different rootstocks except for those grown on RS 193 which gave the least Figure 2.6 shows that there was generally shoot extension on day 42 and day 49. In no marked difference between ungrafted the cold season the least shoot growth was PC 114 plants and those grafted onto observed in PC 114 plants grown on RC /2/99 15/2/ I I, D P C 114 PC 114lRC2 + PC 1141RC3 PC 114lRC4 PC 114/RC6 + PC 1141RS193 PC 114/2270 g 1681RC3 Figure 2.6. Shoot length (mm) of PC 114 composites compared with ungrafted PC 114. Discussion 185, 198 and 213 in another, may be matched together for ease of scheduling. The results obtained from this study have plucking and for leaf quality control in revealed that field cultivars (straight both warm and cold seasons. This would vegetatively propagated) exhibit different be particularly true where mechanical patterns in shoot growth with rootstocks plucking is used. But more work is, apparently having little effect on shoot needed to investigate and compare the growth. In the main growing season PC growth behaviour of different cultivars 81, PC 110, PC 165, PC 168, PC 198 and PC under a wide range of growing 213 had more shoot extension growth conditions, including altitude, fertiliser than PC 105, PC 108 and SFS 150. In the levels and various stages of the pruning cold season SFS 150 showed more shoot cycle. Future studies would also include extension growth than both PC 105 and determining the shoot replacement ratio. 110, which in turn grew more than PC 108. The lack of significant positive influence PCs 185, 198 and 213 apparently showed of rootstocks on shoot extension growth in more shoot extension than SFS 150 both in this study confirms earlier findings, the main growing season and in the cold where Nyirenda (1987) found that shoot season. This shows that these three growth of PC 80 was not enhanced by cultivars and SFS 150, have a much lower grafting onto invigorating rootstocks, base temperature than PC 105, PC 108 and implying that this growth parameter must PC 110. PC 108 appeared to be the most be selected for in the scion cultivar. sensitive cultivar to low minimum However, grafting influenced shoot I temperatures. replacement ratio and shoot density suggesting that future work on composite, These findings suggest that where two or plants should therefore be centred on more cultivars are to be planted in the determining the response of different same field PC 105, PC 108 and, probably, scions to grafting with respect to shoot SFS 150 in one group, and PCs 165, 168, replacement cycle and shoot density.

16 2.5 New released cultivars The following releases were made during the period under review: PC 165, PC 168 and PC 185 in 1998 RC 3, RC 4, RC 5 and RC 6 in 1998 PC 175, PC 184, PC 198 and PC 213 in Publications 1. Mphangwe, N.I.K. and Nyirenda, H.E. (1997). Screening for quality potential in tea clones by chlorophyll fluorescence. Tea Research Foundation (central Africa) Quarterly Newsletter Tea ~eiearch Foundation (Central Africa) Quarterly Newsletter 125, Mphangwe, N.I.K. and Nyirenda, H.E. (2001). New clonal prereleases. Tea Research Foundation (Central Africa) Quarterly Newsletter Tea Research Foundation (Central Afiica) Quarterly Newsletter 142, Nyirenda, H.E. (1997b). Replanting and how to realize maximum benefits from clones and composite plants. Tea Research Foundation (Central Africa) Quarterly Newsletter 125, Nyirenda, H.E. and Mphangwe, N.I.K. (199813). Matching TRF clones for mixing in the field. Tea Research Foundation (Central Africa) Quarterly Newsletter 132, Nyirenda, H.E. and Mphangwe, N.I.K. (2000a). Shoot growth pattern of TRF (CA) clones preliminary results. Tea Research Foundation (Central Africa) Quarterly Newsletter 137, Nyirenda, H.E. and Mphangwe, N.I.K. (2000~). Replanting for maximum total value: Which are the ideal clones possessing high quality and high yielding potential? Tea Research Foundation (Central Africa) Quarterly Newsletter 138, Nyirenda, H.E. (2001). Studies of shoot growth. Tea Research Foundation (Central Afiica) Quarterly Newsletter 141, Nyirenda, H.E. and Mphangwe, N.I.K. (2001). Maximising crop and total value of some TRF clones by plucking at optimum shoot age. Tea Research Foundation (Central Africa) Quarterly Newsletter 143, Mphangwe, N.I.K. and Nyirenda, H.E. (1997). Screening for quality, potential in tea clones by chlorophyll fluorescence. Tea Research Foundation (Central Africa) Quarterly Newsletter 125, Mphangwe, N.I.K. and Nyirenda, H.E. (2001). New clonal prereleases. Tea Research Foundation (Central Afiica) Quarterly Newsletter 142,9 11. TRFCA (2000). Clonal Catalogue